[development] Improve multiple database handling

[Rowan Kerr]

Reference this issue, although I did not create the issue:
http://drupal.org/node/87074

Greetings all :) Nice work on Version 5!

I recently had to make a Drupal 4.6 site connect to a MySQL and a
PostgreSQL database at the same time. Of course, this isn't possible
with the current implementation of database*.inc since the same
functions are redefined in each inc file.

I'd like to update my patch for HEAD and hopefully get this feature
accepted for the next release.

What I actually implemented was two separate features that can be
split into different patches for consideration.
1. Allow connections to multiple different types of database servers.
2. Allow different table prefixes for each database connection.

Hopefully others think this is a useful feature? :)

Again, the issue I'm referring to on Drupal.org is http://drupal.org/node/87074

Thanks,
-Rowan